For years, the success of planetary colonization has resulted in several planets to become inhabited by humans. While the majority of colonies have aligned to form the ISA, the Helghast, a ruthless, militaristic separatist faction have distanced themselves secretly planning to scale an all out war. Killzone takes place during the initial Helghast blitzkrieg of the nearby colony of Vecta. As Vecta City's orbital defenses mysteriously fail, the Helghast have been able to land and deploy their troops rapidly and with ease. As the planetary defense forces become overrun and scattered into the city, the initial objective as an ISA member is to escort a high-ranking official to an evacuation point.